Abstract: An article, forming a toy for a pet or child, includes an enclosure defining a three-dimensional body having an ovoid or spherical shape, an electric motor including a motor body held in place by the enclosure and a drive shaft, and an offset mass element disposed within the enclosure and mechanically coupled with the drive shaft of the electric motor. The article further includes an angular position sensor, an accelerometer sensor, and a control system configured to vary electrical power supplied to the electric motor to drive the drive shaft based, at least in part, on the measurements of angular position of the offset mass element and the angular position of the enclosure to generate rolling motion of the enclosure relative to a surface upon which the enclosure rests.